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I'm writing a hybrid program that sends a struct containing vectors of sprites from the server to the client when a change has been made (New bullets added, new enemy added, enemy or bullet deleted). The program frequently adds several enemies to the vector in the struct.

The sending and receiving of the struct seems to work correctly, but when i attempt to memcopy the struct into the struck on the client program the program crashes. I'm unsure if i have to re-size the struct or how to do this, or if there is another solution to this.

Here is my struct:

struct map{ 
Player Player1;//DECLARE Player SPRITE  

vector<Bullet> Bullets;

vector<Enemy*> Enemies;

}Map;
char Buffer[100];

and this is the function i have is used after the struct has been received:

memcpy(&Map, Buffer, sizeof(Buffer));
MessageBox (NULL, "Memcopied",  "HelloMsg", MB_OK);

I will be very grateful of any help, Thank You

manlio
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Staarland
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    You need to marshal and unmarshall. [Protobufs](https://developers.google.com/protocol-buffers/docs/reference/cpp/index) for example. – Remus Rusanu Jan 03 '13 at 20:32

2 Answers2

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Looks like Player and/or vector are not only on the stack but have themselves pointers to somewhere else like on the heap to store all your information. So these pointers will be dangling once you unpack your message. You should try and design your own data format where all information is neatly placed along the memory.

s.bandara
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Old C functions as memcpy and memset are good for POD structs but they are very dangerous for structs/classes that contain such "complex" objects as std containers. Memcpy copys objects simply byte by byte. However std containers include pointers to memory in heap and when you are copying them with memcpy you get two objects pointing to the same memory. When one of them is destroyed another one still points to deleted memory. It causes the crash. I think you need to some specific type to pass the data from server to client.

fsquirrel
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